In stereo audio reproduction, crosstalk refers to signals leaking from one channel to another. For example, signals in the left audio channel and the right audio channel may leak into each other, causing a reduction in channel separation.
Audio devices often include a jack (i.e., socket), such as a headset jack, for receiving a media plug such as a headset plug of a headset. For example, such audio devices may include, but are not limited to, mobile phones, MP3 players, handheld gaming devices, tablets, personal computers, laptop computers, and all kinds of media devices that generate audio signals.
A headset combines a headphone with a microphone. The position of the microphone terminal may vary across different types of headset plugs. An audio device may be configured to accommodate different types of plugs; for example, a 4-pole plug of a European type or a North American type. According to the European type plug layout, the plug terminals are ordered as left audio (L), right audio (R), microphone (M), and ground (G), as enumerated from the tip to the base of the plug. On the other hand, according to a North American type plug layout, the plug terminals are ordered as L, R, G and M. To accommodate the two types of plugs, a media device typically includes a swap switch that can swap the connections of the M and G plug terminals to its internal circuitry. However, the swap switch may cause crosstalk between different channels of the media device, as explained below with reference to FIGS. 1A, 1B and 1C.
FIG. 1A illustrates a 3-pole plug 110 that has three plug terminals: L, R and G, as enumerated from the tip to the base of the plug 110. The plug 110 is connected to a 3-pole headset jack 120; only the jack terminals 125 and a portion of its internal circuitry is shown. The jack terminals 125 are labeled by 1, 2 and 3, corresponding to L, R and G plug terminals, respectively. To prevent crosstalk between the L and R audio channels, the headset jack 120 includes a connection, referred to as HP_Sense, to connect the amplifier inputs to the ground connection (i.e., the G plug terminal). The HP_Sense serves as a common reference point for the L and R audio channels.
FIG. 1B illustrates a European type headset plug 130 and FIG. 1C illustrates a North American type headset plug 140, both connecting to a 4-pole headset jack 160. A swap switch 150 is coupled to the 4-pole headset jack 160 to accommodate different types of 4-pole headset plugs. In FIGS. 1B and 1C, HP_sense is no longer connected to the G plug terminal directly; it is connected to the G plug terminal via the swap switch 150. The resistance of the swap switch 150 (Rsw) increases the crosstalk between the L and R audio channels. One approach to the crosstalk removal is to replace the swap switch 150 with multiple switches such that the path labeled “ADC” and the path labeled “HP_Sense” are both connected to both jack terminal 3 and jack terminal 4 via these switches. By controlling the on/off of these switches in accordance with the type of the plug, HP_Sense can be directly connected to the G plug terminal for either type of headset plug. However, potential Electromagnetic compatibility (EMC) problems may occur when integrating these switches into a system-on-a-chip (SOC). Incorporating extra balls and beads to the chip may overcome the EMC problems but may add significant hardware cost.
Moreover, none of the existing approaches address the issue of crosstalk from the L and R audio channels to the microphone channel. Therefore, there is a need to mitigate the aforementioned crosstalk problems with a more comprehensive and cost-effective approach.